1. Field of the Invention
The present invention relates to an injector that injects fuel.
2. Description of Related Art
A conventional injector has a valve member and a valve body that supports the valve member such that the valve member can move inside the valve body in an axial direction. An inner wall surface of the valve body and an outer wall surface of the valve member define a fuel passage therebetween. The valve body is formed with a valve seat section on the inner wall surface and with a recess portion downstream of the valve seat section. Injection holes are formed in the recess portion. The valve member has a seat section. The seat section is seated on the valve seat section to stop fuel injection from the injection holes. The seat section separates from the valve seat section to allow the fuel injection from the injection holes (for example, as described in Patent Document 1: JP-A-2000-314359). In this kind of injector, an end face of the seat section of the valve member is located to face the recess portion of the valve body, thereby defining a fuel chamber (which is referred to also as a sack section) between the recess portion and the end face of the seat section.
The device described in Patent Document 1 as a kind of such the injector has a single injection hole in the shape of a slit, i.e., an injection hole in the shape of a flat fan. The injector forms a fuel spray, which is injected from the injection hole, in the shape of a liquid membrane spreading flatly in a lateral direction in the shape of a fan. This technology uses a high penetration force (i.e., heightened injection velocity of the fuel) to form the liquid membrane of the fuel spray in the shape of the flat fan, thereby increasing a contact area between the liquid membrane and a surrounding air. Eventually, atomization of the fuel is enabled by friction between the liquid membrane and the surrounding air.
A device described in Patent Document 2 (JP-A-H11-70347) as another type of the injector is formed with multiple injection holes on the tip side of the valve body, i.e., in the recess portion. This technology improves the degree of freedom of formation of the fuel spray shape by injecting the fuel from the multiple injection holes. For example, the technology forms the fuel spray in the shape of the flat fan as described above or in a conical shape.
With the conventional technologies of Patent Documents 1 and 2, it is expected that the atomization of the fuel can be attained while diffusing the fuel spray in a cylinder when the fuel is injected directly into a combustion chamber of a cylinder (hereinafter, referred to simply as a cylinder inside) of an internal combustion engine. If the high atomization is aimed at, it is necessary to further increase the injection velocity from the injection hole, i.e. the penetration force. In this case, there is a concern that the injected fuel (i.e., the fuel spray) adheres to wall surfaces inside the cylinder such as a cylinder wall surface. The inventors consider that it is because a tip of the spray maintains an internal energy without splitting and therefore the velocity at the spray tip is less apt to fall in the conventional technologies of Patent documents 1 and 2.
If the injected fuel adheres to the cylinder wall surface the fuel turns into an unburned gas such as HC and can cause increase of smoke during a start from the cold state or the fuel adhering to the cylinder wall surface dilutes oil providing lubrication between a piston and the cylinder wall surface.